Conventionally, there has been known a seat sliding apparatus for a vehicle disclosed in JP2005-47347A. This seat sliding apparatus for a vehicle includes, as shown in FIGS. 9 and 10, a lower rail 110 fixed on each side in a width direction of a vehicle floor, an upper rail 120 fixed on each side in the width direction of a seat of the vehicle, and steel balls 130 and 131 disposed between the lower rail 110 and the upper rail 120 to enable the upper rail 120 to be movable relative to the lower rail 110 in frontward and rearward directions in a longitudinal direction of the lower rail 110. FIG. 9 is a cross-sectional view of a pair of the lower rail 110 and the upper rail 120 arranged on either one side in the vehicle width direction, and FIG. 10 is a perspective view of the upper rail 120.
As shown in FIG. 9, the lower rail 110 having a substantially U-shape in cross section includes a base bottom portion 110a horizontal to the vehicle floor, first side portions 110b extending upward from the opposite ends of the base bottom portion 110a, upper portions 110c extending inward from respective upper ends of the first side portions 110b, and second side portions 110d extending downward from respective one ends located at an inner side of the upper portions 110c. The upper rail 120 having a substantially reversed U-shape in cross section includes a base plate portion 120a substantially parallel to the base bottom portion 110a of the lower rail 110, vertical portions 120b extending downward from the opposite ends of the base plate portion 120a, connection portions 120c extending outward from respective lower ends of the vertical portions 120b, upright portions 120d extending upward from respective one ends located at an outer side of the connection portions 120c, and tilting portions 120e tilting inward from respective upper ends of the upright portions 120d. Each steel ball 130 is provided in contact with the first side portion 110b and the upper portion 110c of the lower rail 110 and the tilting portion 120e of the upper rail 120. Each steel ball 131 is provided in contact with the base bottom portion 110a and the first side portion 110b of the lower rail 110 and the connection portion 120c of the upper rail 120. These steel balls 130 and 131 are held rotatably by retainers 140. Further, as is also shown in FIG. 10, the upper rail 120 is integrally formed with guides 150 made of resin and each inserted between each first side portion 110b and each second side portion 110d of the lower rail 110. Between the front end portion and the rear end portion of each guide 150, a recess portion 150a is formed into a recessed shape and along which the retainer 140 is movable.
According to the seat sliding apparatus for a vehicle described above, the guide 150 inserted between the first side portion 110b and the second side portion 110d of the lower rail 110 is integrally formed with the upper rail 120. Thus, the upper rail 120 can be prevented from deforming. Further, since the movement of the retainer 140 is restricted within the recess portion 150a, the balls 130 and 131 can be prevented from slipping out of the upper rail 120.
However, in the conventional seat sliding apparatus for a vehicle described above, two guides 150 and four retainers 140 are required for one pair of the lower rail 110 and the upper rail 120. This results in increased number of parts. Further, in this seat sliding apparatus for a vehicle, although the balls 130 and 131 are prevented from slipping out of the upper rail 120, no countermeasures have been taken to prevent the balls 130 and 131 from slipping out of the lower rail 110. Thus, in order to prevent the balls 130 and 131 from slipping out of the lower rail 110, it is required to provide eight stoppers in total (two stoppers for each retainer 140) at the lower rail 110 for one pair of the lower rail 110 and the upper rail 120 after assembly, which may cause a post-process to be difficult.
The present invention has been made in view of the drawbacks described above and thus a need exists for a seat sliding apparatus for a vehicle having a reduced number of parts and providing an easier post-process.